This invention relates to imaging systems and more particularly to systems suitable for dental X-ray diagnosis where the system may be used to produce panoramic radiographs of the jaw of a patient.
In conventional dental X-ray systems for producing panoramic radiographs, an X-ray source is directed at the patient and an image recorded on a moving X-ray film. A secondary diaphragm having a slot is located in front of the X-ray film as an aperture to define the part of the film where the radiation-is incident. It has previously been proposed to replace the moving X-ray film by a CCD sensor. In this system, a unit is used which is rotatable about a vertical axis and which carries an X-ray source at one end of an arm and a CCD sensor at the other end of the arm located behind a secondary diaphragm. The secondary diaphragm includes an opening or secondary slot which acts as the aperture.
According to a first aspect of the invention, there is provided an imaging system for dental use comprising: a source of X-ray radiation; solid state detector means having a radiation sensitive region which includes an image area at which charge accumulates which is representative of incident radiation, the extent of the image area being defined substantially solely at the detector means: means for moving the source and detector means relative to a subject to be examined, in which the subject is arranged to be located between them and means for processing the output of the detector means to obtain a panoramic image of the subject.
The inventor has realised that the secondary slot previously considered to be an essential feature may be eliminated from the system without causing image quality deterioration to such an extent that it is no longer satisfactory and in certain cases that elimination of the secondary slot may improve image quality.
The image area is defined substantially solely at the detector means and obviates the need for a secondary slot or opening in a diaphragm to be used to define the aperture area as required in the conventional moving X-ray film arrangement or the previously proposed CCD sensor systems. This produces a more simplified system compared to previously known arrangements which is less bulky and allows for more precise control of the alignment and movement of the arrangement, improving reliability. Also, use of the invention facilitates assembly and eases design constraints. In some situations a secondary slot may be responsible for generating scattered radiation which degrades the image. Elimination of the slot by employment of the invention can thus improve image quality.
In one advantageous embodiment of the invention, the detector means includes scintillator material carried on its surface for converting X-ray radiation into radiation of another wavelength for detection by said detector means and the image area is defined at the detector means by the extent of the scintillator material on the detector means. The scintillator material which converts incident X-ray radiation into a wavelength to which the detector means is responsive may be carried directly by the surface of the detector means or on an intermediate layer laid down on the detector means.
In another advantageous embodiment of the invention, the extent of the image area is defined by the location of charge storage means at which radiation is incident to cause the accumulation of charge. Thus, where the detector means is a CCD sensor array, the location of charge storage sites defines the image area. Scintillator material may be used on the CCD array in register with it to further define the image area extent or could alternative extend beyond the charge storage sites in one or more directions.
It may be advantageous in some embodiments in accordance with the invention to include shielding material on the surface of detector means surround in the scintillator material to absorb stray X-ray radiation. Preferably the solid state detector means is a CCD array but other types of sensor may be used.
According to a second aspect of the invention, an imaging system for dental use comprises a source of X-ray radiation; solid state detection means having a radiation sensitive region which includes an image area: means for moving the source and detector means relative to a subject to be examined, the subject being arranged to be located between them: and means for processing an output of the detector means to obtain a panoramic image of the subject, and wherein no secondary slot is located in front of the detector means.
According to a feature of the invention, there is provided solid state detector means for use in an imaging system in accordance with the invention.